How to correct twin disc pattern cock-up?

Very irritating afternoon. Did a tray test this afternoon behind our twin-disc spreader applying Nitram at 24m and 375 kg/ha. Had this spreader tested by a specialist firm and had it set up well on Nitram two years ago (didn't use it much last year). Today this was the result (far left at 0m from tramlines, next to the right at 4m, next at 8m and furthest right at 12m from the tram-lines):

We did another tray test using a different bag, with a different amount in the hopper, after checking the settings and on both sides of the tram-line and got the same result. How can it be this far out?!

The scale on those Amazone gauges is non-linear which I find a bit illogical. Anyway, it's clear that we were applying at least twice as much behind the spreader compared 8m out from the tram-lines. I'm kicking myself, but I only did this test after we've done quite a few acres. The question now is how the hell to correct this cock-up?

It will probably mean that our total N rate so far various between 180 and 220 kg/ha. Should we just bump the late N dose for protein up by 20 kg/ha and accept the variation, or should we try and tweak the spreader so that it applies more in the middle of the tram-lines and less behind the tractor to try and compensate? Another idea is to get some liquid fert and apply in bands where the rate was lower.

The few tray tests I did last year were always an annoying amount out - never less than 5% variation and often quite a bit more. With our newer spreader you take readings off the gauges, put the values into the computer and adjust the discs accordingly. Did that for Nitram last year and even after the correction I had to recorrect.

All this has convinced me that we're going to switch to liquid fert asap. I don't care what the price difference is - at those levels of inaccuracy there can be no argument. We were using high quality expensive solid fertiliser, new vanes on the spreader and very light wind.

I would try and tweak the spreader. Were you really applying 375kg/ha? or 75?
Ideally the shorter vane needs replacing with a longer version.
Even if it takes you a day fissing about with the spreader to get the totals correct it is probably the easiest way to sort it.

I would try and tweak the spreader. Were you really applying 375kg/ha? or 75?
Ideally the shorter vane needs replacing with a longer version.
Even if it takes you a day fissing about with the spreader to get the totals correct it is probably the easiest way to sort it.

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375 kg/ha of product (129 kg/ha of N). I think you're right though. I'm going to enter false values into the Amatron 3 box on the other spreader to get it to help me guess what vane settings to start with to produce an uneven but inverse pattern to correct.

Leave it as it is and drive in between the tramlines with very narrow wheels on.

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That was another suggestion. We have got row crops which are pretty narrow. Rather embarrassingly we've done 300ac or so like this. Kicking myself for thinking it would be OK from the previous year and not checking before we started.

That was another suggestion. We have got row crops which are pretty narrow. Rather embarrassingly we've done 300ac or so like this. Kicking myself for thinking it would be OK from the previous year and not checking before we started.

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To be honest I think it'll be the simplest solution. The wheat will stand up again anyway with only one pass over it.

Used to use liquid many years ago with success until our contractor let us down one year about a week before he was due to spread the stuff. Would go back to liquid tomorrow if I could guarantee the supply and a good contractor to put it on; so much better than granular spreading in terms of evenness of application on border cut off etc.

Can't remember quite how you do it, but i think if you press scales and C together the pulses should open to 1500 on each side.
If you walk around the back of the spreader both slides should be on 40-41.
If they are different you need to adjust them so they both read those numbers.
Found this out earlier in the year when ours was putting different amounts through each side.

Can't remember quite how you do it, but i think if you press scales and C together the pulses should open to 1500 on each side.
If you walk around the back of the spreader both slides should be on 40-41.
If they are different you need to adjust them so they both read those numbers.
Found this out earlier in the year when ours was putting different amounts through each side.

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Yes, already had that problem on the newer spreader. Had to buy a little tool from Amazone (at great cost as usual) to check the spacing. This pattern problem has happened with the older spreader.

Yes, already had that problem on the newer spreader. Had to buy a little tool from Amazone (at great cost as usual) to check the spacing. This pattern problem has happened with the older spreader.

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That's been a problem on Amazone spreaders since the year dot.
Old fashioned non variable/weigh cell ones told you to put something like an 8mm drill bit through the apeture opening on a set setting and then adjust to get same slide setting on each side.

Amazone must have worked out if you can afford a fancy all singing all dancing spreader then you will stretch to a bit more for an expensive little tool to cure their design flaws.

Glad I've just got a bog standard Kuhn Axis now. Not that much to go wrong, Linear scale settings and seems to be far more forgiving if set slightly out.
All with no buggering about adjusting vane settings

Is it a za-m spreader? Increasing the short vane position will throw the fert away from behind the tractor but by how much to adjust it would be trial and error, was your machine set level? Never had any problems with blue bag spread patterns personally, did the fert look in good condition?

It looks almost as if one of your discs is applying massively more than the other. The tray on the tramline is very full, the other three are fairly similar.
Was one side of the spreader emptying before the other?

You could do with doing a proper tray test, 12 trays spaced out evenly between two tramlines. Drive up one tramline and back down the other. Weigh them all and see what the full spread looks like.